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The Wieliczka Salt Mine of Poland was included in the first UNESCO World Heritage list in 1978. It is also on the Polish List of Historic Heritage and, when visiting, provides an interesting way to get to know how salt has been mined underground for almost nine centuries. In the summer, almost 8,000 tourists a day visit Wieliczka, which has 500 tour guides and 400 miners maintaining the mine. After buying your ticket, you are allotted a guide who will take you around the mine. Patrycya, our guide, has been on the job for 20 years and we enthusiastically followed her to explore the beauty, material culture and historic heritage of the mine and its excavated complex.

Fig. 1. Kinga – the patroness of the miners, along with other salt sculptures.

We opted for the tourist route, which lets you explore chambers, galleries, chapels and lakes. The mine has been opened to the public with this route since the end of the eighteenth century and has more than 300km of galleries and almost 3,000 chambers. It is divided into nine floors at depths varying from 64m to 327m. We went down to the third floor, which is at a depth of 135m. To get to the first level, one has to walk down 380 wooden steps, but the walk is comparatively easy. There are a total of 800 steps that tourists walk in the mine and, after the tour ends, a lift takes you to the exit in a mere 40 seconds.

The grey rock ceiling of the first floor is a national treasure, made of impure salt which is 95% sodium chloride and 5% different impurities. It is these impurities that give the salt its grey colour. In the past, this salt without being purified was used to preserve food. It is edible and contains good quantities of minerals. In subsequent chambers of the mine where this grey salt is present on the walls, tourists can lick it (if they want to risk it) to deduce for themselves that it is indeed salt. The first chamber that we entered is known as the Urszula Chamber and it shows how miners used simple hand tools to extract salt between 1649 and 1685.

Fig. 2. The Nicholas Copernicus salt monument, dedicated to the well-known Polish astronomer.

There is a hoisting device, which was operated by four miners who walked round and round it, pushing it forward to wind the rope around the vertical axel to lift a heavy block of salt. This process was used to transport salt from the second to the first level, as the shaft was 30m deep. The floor is also made of salt and, in many tunnels and chambers of the mine, there is a solid salt floor or salt tiles, which get polished by visitors walking over them.

Fig. 3. Salt on the walls.

At a depth of 64.4m, we entered the Nicholas Copernicus Chamber. Nicholas Copernicus was the well-known Polish astronomer, who has been credited with formulating the heliocentric model of the solar system. It is believed that he visited the mine in 1493, when he was studying in Krakow. At that time, he was 20 years old. The floor, ceiling and walls of this chamber are all made of salt.

Fig. 4. Simple tools which were used for salt mining. Fig. 5. Urszula Chamber showing how miners used simple hand tools to extract salt.

In the centre of the chamber, there is a monument dedicated to Copernicus. Carved in salt in 1973 by Wladyslaw Hapek, the monument marks the 500th anniversary of his birthday. In the past, this chamber was a single huge block of salt. Usually, there are layers of salt under the ground, but, in the upper part of the deposit, there are no layers. The miners dug in the soft rocks of clay and shale to find a block of salt. The chambers in the mine are of varying shapes and sizes, as this depended on the sizes and shapes of the blocks of salt that the miners found underground.

Fig. 6. Salt stalactites that worry miners as they mean that water is leaking.

In the next chamber are six life-size salt sculptures that depict how rock salt was discovered in Poland. The legend goes that Kinga was a Hungarian princess and was engaged to marry a polish duke. As a dowry, she was given a salt mine in Marmaros. At this time, salt was very precious and Poland suffered from a lack of it. Kinga, learning of this, decided to give salt to Poland as her wedding present. She threw her engagement ring in the mine and in Wieliczka, Kinga ordered the miners to dig in a specific spot. Her ring was found in the first salt block unearthed and salt has been found in abundance in Poland ever since. Kinga is the patroness of the miners.

Fig. 7. Salt sculptures in one of the many chambers of Wieliczka Salt Mine.

Long and thin salt stalactites can be seen at one corner of the chamber and these are a cause of worry to the miners, as it means water is leaking through the mine. The miners collect the water and bring it to the surface to produce salt. About 15,000 tonnes of salt is manufactured in a year. In other chambers of the mine, we found white salt, which is pure sodium chloride and it crumbled when we touched it.

Fig. 8. Tourists exploring the mine as they pass through its grey salt walls.

This is the first part of a two-part series about this fascinating mine. In the second part, I will deal with the geological origin of the mine, the use of horses there almost 400 years ago, the St Anthony’s Chapel, the Holy Cross Chapel and the biggest and grandest chapel of all the Wieliczka Salt Mine – the St Kinga’s Chapel.

All photographs by Khursheed Dinshaw.

Khursheed Dinshaw (India)


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The Tully Monster Mystery

The Tully Monster is a mysterious 307myr-old marine animal known only from the famous Mazon Creek fossil locality in Illinois. Its body plan is unlike any other animal that has ever lived, and it has been subject to wildly different interpretations as to its identity since its discovery in 1955. Last year, Victoria McCoy of Yale University and colleagues identified it as a lamprey, a primitive type of fish, but this has since been challenged by a team of vertebrate palaeontologists.

Fig. 1. Reconstruction of a Tully monster based on the research of McCoy and colleagues. The claw and proboscis are on the right and its eyebar and eyes, gills and tail fin are further back. (Sean McMahon/Yale University.)

Fossil collector Francis Tully knew he had made an extraordinary discovery. Inside a rounded nodule was a bizarre, foot-long animal with a long trunk and claw. But he could never have known quite how extraordinary his 307myr-old fossil would turn out to be. Sixty two years later, scientists are still arguing over the basics as to what sort of creature it really was.

What makes it even stranger is that this is no rarity known only from fragmentary remains. After Tully made his find, word got around among collectors and, before long, hundreds more had been found. Tullimonstrum gregarium, or ‘Tully’s common monster’, is now known from well over a thousand fossils, including many complete specimens. “We’ve got four cabinets of Tully monsters here, each of which has 25 drawers,” says Paul Mayer of the Field Museum in Chicago, where the largest collection is held.

Common, well-preserved and complete fossils should be the very easiest to identify. So why has this one remained so enigmatic? And how did it acquire such notoriety that the MailOnLine recently suggested it was the ‘weirdest animal that ever lived’?

Tully, a pipe-fitter by trade, discovered the fossil in a pile of nodules discarded from a coal mine in the Mazon Creek area of Illinois. “One day in the summer of 1955 I found two rocks that had cracked open due to natural weathering. They held something completely different. I knew right away, I’d never seen anything like it. None of the books had it. I’d never seen it in museums or at rock clubs. So I brought it to Chicago to the Field Museum to see if they could figure out what the devil it was,” said Tully in an interview with the Chicago Tribune in 1987.

Fig. 2. Tully monster fossil in an ironstone nodule. Its head is on the right and its tail is on the left. Actual life-size. (Thomas Clements/Burpee Museum of Natural History.)

Weathering had split the nodule to reveal a creature with an elongated squid-like body and tail fin that was fronted by a long thin snout with a toothed claw at the end. Widely spaced eyes projected from a pole-like structure that stuck out on either side of its body. This body plan is different from any other creature that has ever lived.

Tully showed his fossil to Eugene Richardson, the curator of fossil invertebrates at the Field Museum, who was also baffled by the find. Fossil-rich ironstone nodules were found in shale beds that lay on top of coal deposits. Miners would move the shale and nodules aside to get at the coal which allowed collectors to scour the spoil heaps for fossils. Before long, hundreds more specimens had come to Richardson’s attention, but he was still none the wiser as to what it was.

Fig. 3. Tully monster photographed in polarized light. At the top, its proboscis has folded back over its body, while the dark spot projecting out is one of its eyes. Muscle blocks run along its body (as identified by McCoy and challenged by Sallan), while its tail fin is at the bottom. This is the ‘holotype’ specimen used when the species was first described. (Nicole Karpus/Field Museum.) Fig. 4. Tully monster in polarized light. This one is folded in two, with its claw lying over the end of the tail at the bottom. Its eyebar and eyes are on the left, while the tail fin spreads out bottom right. Scale bar in inches. (Paul Mayer/Field Museum.)

Measuring between 8cm and 40cm long, the Tully monster has only ever been found at sites around the Mazon Creek, a tributary of the Illinois River, in north-eastern Illinois. The Mazon Creek is world famous for its abundant fossils of soft-bodied animals, which are not normally preserved. The site provides palaeontologists with the most complete snapshot known of the creatures that lived during the Carboniferous period of 359 to 299mya.

Fig. 5. Partial Tully monster, with its proboscis folded over. Its eyes project out on an eyebar at the top. The claw is not visible in this specimen. Yellow scale bar equals 1cm. (Paul Mayer/Field Museum.) Fig. 6. Partial Tully monster showing striping that may be muscle segments. The eyes and eyebar are visible at the top. (Paul Mayer/Field Museum.)

The Tully monster lived in a large estuary alongside jellyfish, sea anemones, a wide variety of marine worms, different types of mollusc, shrimps, horseshoe crabs and other arthropods, as well as several kinds of fish – lungfish, ray-finned and spiny-jawed fishes, coelacanths and sharks. Leaves and branches of land plants were also washed by a great river into the estuary, where it flowed into a shallow sea.

Fig. 7. This free-swimming sea snail, a type of heteropod mollusc known as Pterotrachea, arguably looks more like a Tully monster than any other living animal. Palaeontologist Merrill Foster proposed in 1979 that the Tully monster was a strange type of sea snail comparable with, but not directly related to, the heteropods. Some scientists still believe this to be the case. In this photo, its black eyes are above its proboscis and mouth on the right. Its rounded swimming fin hangs down centre-left and its internal organs are visible. (Dante Fenolio/Science Photo Library.)

On land, swampy tropical forests dominated by giant clubmoss trees, seed ferns, horsetails and true ferns were home to amphibians and a rich variety of insects and other arthropods. Waterlogged soil in these forests created low oxygen conditions that inhibited the decay of  dead trees and plants,  which eventually resulted in the coal seams that were mined in modern times. The climate was hot and sticky and the site was located just ten degrees from the equator.

The fossils were formed when a colossal flood dumped huge amounts of sediment into the river delta. Animals living on the sea floor were smothered, while swimming creatures were jumbled up with plants and insects from land in a muddy grave. Very low levels of oxygen meant the buried organisms were not subject to rapid decay. Instead, bacteria slowly decomposed the remains, while emitting methane and ammonia, and triggered a series of chemical reactions that eventually resulted in nodules forming around the fossil nuclei.

Fig. 8. The eye structure of the Tully monster, as seen under a scanning electron microscope. This arrangement of ‘meatball’ and ‘sausage’ shaped melanosomes has only ever been seen in animals with backbones and provides evidence for the Tully monster also being a vertebrate. 1μm equals one thousandth of a millimetre. (Thomas Clements.)

Most Tully monster fossils came from Pit Eleven of the Peabody Coal Company strip mine near Essex in Illinois, located 105km southwest of Chicago. Nodules preserve the soft-bodied invertebrates as well as easier-to-preserve shells, fish skeletons, arthropod exoskeletons and plant leaves and twigs.

Fig. 9. Bizarre, elongated prey-capturing snouts are occasionally found in fishes. The snout of this Australian ghost shark bears some similarities with the Tully monster’s clawed proboscis. (Fir0002/Flagstaffotos; http://www.gnu.org/licenses/old-licenses/fdl-1.2.html.) Fig. 10. The stalked eyes of this black dragonfish larva are every bit as alien as those of the Tully monster. (G David Johnson/Smithsonian NMNH.)
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Inspired by the recent excellent series of articles by Trevor Watts discussing the types of Mid-Jurassic dinosaur footprints to be found along the Whitby coast (Deposits, Issues 46, 47, 48 and 49), when recently working in the area I (NL) made sure that I would have the time to walk the beaches from Saltwick Bay to Whitby. I also timed my work to make sure I could make use of the low tides early in the morning at first light. As well as the usual ammonites, belemnites and plant fossils, I found a handful of single footprint casts (most too heavy to attempt to move) and some very nice fallen slabs of claw marks and partial trackways – also mostly too big to move. One slab in particular stood out among the others at the bottom of the Ironstone Ramp in Long Bight (Figs. 1 and 2) – a ‘double trackway’ from what look like two quite different beasts walking in parallel – although they were possibly formed at different times. In the form of raised footprint casts rather than actual indented footprints, the specimen included five good prints in the left track and four, possibly five prints, on the right track – so each track contained a ‘full set’. Although the tracks look superficially quite different from one another, both appear to be attributable to theropod dinosaurs.

The slab was not buried in the sand, but sat on some other fallen blocks so could be seen in its entirety. However, at about 1.2m x 1.0m x 0.2m, it must have weighed in excess of 500kg. To ‘collect’ it, one option was to break it up and take it away in pieces in several visits and put it back together again at a later date, but that would have been less than ideal to say the least and small fragments might have been lost. A preferable option would have been to carry the complete slab all the way back to Whitby in one piece, requiring a group of people walking along the beach at low tide. The first five metres or so would have been a difficult scramble over all the other fallen blocks while carrying the heavy weight, but it would have been possible to do this relatively safely by using beams of wood to lever the slab carefully onto a strong pallet, then sliding the beams inside the pallet and carrying it away ‘stretcher’ fashion – if enough people and time had been available. However, ‘Storm Doris’ was about to hit and the chances were that the specimen would be broken into pieces by the next day. Even if it survived the storm, it was possible that, although most people finding it would admire the specimen, maybe take photos and then leave it where it was, someone else might take a hammer and chisel to it and try to remove the nicer of the raised footprints on the left side of the block.

Fig. 1. The slab from the Saltwick Formation containing the two trackways found at the base of the Ironstone Ramp in Long Bight, east of Whitby. (N Larkin for scale.)

The best option – which did not preclude returning at a later date with a gang of people to collect the specimen for the local museum if it survived the storm – was to take as many photos as possible there and then to record the specimen. This would involve not just taking the pictures with something included for scale (as well as the obligatory ‘selfie’) but taking photos from as many angles as possible from approximately the same distance, including around the back and underneath as far as possible, specifically so that a photogrammetric 3D digital model could be made of the specimen at a later date. The problem was that the only camera I had on me was a rather old ( about 2013?) and cheapish mobile phone with limited memory. So I took 65 photos with this. I returned the next day to find that the specimen had thankfully survived Storm Doris and I took 81 more photos, this time with a proper digital camera (a Canon Powershot SX50 HS).

Fig. 2. One of the prints from the track on the left.

Not only did this mean that the double trackway was well recorded before it got damaged, but it also meant that two digital photogrammetric models could be built, one from each set of images. It would also be interesting to compare the two models to see if the old mobile phone camera would provide something useful or whether this sort of photogrammetric work can only be achieved with a ‘proper’ digital camera. To ensure the best chance of good digital models being made from these images, I sent the photos to Steven Dey, a photogrammetry, laser-scanning and 3D-printing expert at ThinkSee3D based in Oxfordshire, with whom I have worked on many palaeontological projects before. Below, he describes the processes of making the 3D digital models, as well as giving top tips for taking good photogrammetry photos in the field.

Photogrammetry (also known as SfM – Structure from Motion) generates digital three-dimensional models from multiple photographs taken from different positions and angles around an object. An advantage of photogrammetry compared with other methods, such as laser scanning, is that the ‘scanning’ part of the process is very cost effective as all that is needed is a digital camera to capture the data and even a mobile phone camera will do. This means it is an ideal method for use in the field, when out looking at large specimens and geological features. It is even possible to take accurate measurements of the resulting digital 3D specimen and to measure features, particularly useful if the specimen itself was difficult to access. To ensure this, place a scale bar or an object of known size (a geological hammer, hand lens or trowel for example) on the specimen in a few photographs to act as a reference and this will allow the digital 3D model to be made with a relevant scale. You can also put a colour scale in the scene, so the colours of the phototexture can be colour balanced if you want accurate colour reproduction.

Informal comparative trials have shown that the accuracy of virtual 3D models of fossils produced with photogrammetry can be equal to or even better than other scanning methods, but this accuracy is dependent on four main influences: (1) the quality of the photography; (2) the quality of the light in the environment; (3) the surface quality of the specimen; and (4) the processing of the images into a 3D model.

  1. The quality of the photography

Most considerations are common to all photography, such as reducing camera shake (a tripod can help), good focus and an appropriate exposure to minimise over-exposed or under-exposed areas. However, some considerations are particularly relevant to the photogrammetry process, such as ‘depth of field’. Oblique angled photographs across a specimen, especially a long object, can be partly out of focus due to a limited depth of field if care is not exercised, so avoid overly oblique shots. ‘Shutter priority’ can be a useful setting on a digital camera for photogrammetry, as this allows the ‘f’ number to be tuned to maximise the depth of field.

Fig. 3. The various positions (the blue rectangles) of the mobile phone used to model the slab.

Distance from the subject is also worth considering. Normally, with a standard 50mm lens, a distance of around 0.5m or so works well. Too close and lens distortions can cause issues. Too far away and the resolution of the images – and therefore the resolution of the eventual model – will be reduced. The resolution of the digital model is directly related to the distance from the subject, and to the size and resolution of the image sensor in the camera. An ‘auto’ setting on the camera can normally be an appropriate facility to use, but it can also be a problem if very different brightness levels are experienced in different areas of the specimen, for example, sharp differences in light and shade on a sunny day. Rarely are conditions ideal in the field, so it is worth trying a few configurations of camera settings if there is time and, if you have such options, taking test shots from different angles and reviewing them before taking the final set of images all on the same setting.

A definite departure from normal photography is the need to capture multiple photos from numerous angles around the subject. Every angle of the specimen that needs to be scanned has to be captured with an 80% overlap between photos. Fig. 3 shows the various positions (the blue rectangles) of the mobile phone used to model the trackway slab on the coast at Whitby. To have captured the whole of the specimen, it would have been necessary to scan one side first, then turn it over and scan the underside, but this could not safely be undertaken with such a heavy slab. As an example, however, this was easily done for the 32kg single sauropod footprint cast collected on the same day using just 45 photos (Fig. 4).

  1. Light quality

The perfect conditions for taking photographs for photogrammetry purposes are bright diffuse light, such as being outside on a cloudy day in the spring or summer, as changing light, dark shadows and/or bright sunlight on surfaces are not ideal. Highlights from bright sunlight tend to move position between different photographs, and shadows obscure the surface colours and texture of the specimen. Both of these would lead to ‘noise’ and inaccuracies in the final 3D model. If indoors, use diffused daylight from windows or artificial ‘daylight’ lighting, or set the camera to compensate for electric lighting.

  1. Surface quality

Photogrammetry works best with highly textured subjects. It does not work on very shiny objects, or transparent or very monochrome objects. For example, a very plain white wall would not scan, as the algorithms in photogrammetry need to see features ‘moving’ from image to image to determine depth. If those features do not exist or reflective highlights move between shots, the process of building the virtual model will fail. The highly-textured surface of fossils, such as footprints and their surrounding rock is particularly suited to photogrammetry, as the algorithms involved rely on differences in surface colouration and texture to recreate the 3D geometry.

  1. Processing the images. Processing the data efficiently requires a computer with a reasonably high specification, such as my (SD) Intel i7 with 32Mb RAM and a good GPU card (for example, NVIDIA). Even then, processing photographs into 3D models is an extremely computing-intensive process, often requiring many hundreds of millions of calculations. So, if there are a lot of photos, it is sometimes necessary to reduce the resolution. Photogrammetry software can help by allowing the data to be broken into blocks to process it in smaller sets and thereby not overwhelming the computer’s resources all in one go. The software we used was Agisoft Photoscan standard edition.
Fig. 4. 3D model of the single sauropod footprint cast collected on the same day, made using just 45 photographs.

Weaknesses in any of the above four factors can lead to ‘noise’ in the final virtual model or lower resolution of detail, or, in extreme cases, failure to create the 3D model. It is usual for some of these factors to be imperfect, so compromises have to be reached, but the photogrammetry process itself is quite robust and can sometimes cope with quite poor inputs. In reasonable conditions, much larger specimens than the footprint slab can be captured this way, even large geological features and indeed whole landscapes. Virtual 3D models can even be made from photographs taken underwater, taken by drones or other aerial photography and even microscopic photogrammetry is possible – as long as enough good quality photographs are taken in good conditions. But 3D model processing considerations have to be accounted for. It might take many hours to process a very large set of photographs into a 3D model, depending on the specification of the computer.

The whole scene of the Whitby footprint slab as a 3D model without the colour overlay is shown in Fig. 5. The output of the process is effectively a 3D photograph of the scene. The texture file overlays multiple photo images on to the 3D geometry adding data on the surface colouration. Looking at the model without the colour overlay can sometimes reveal morphological features that are otherwise hard to distinguish.

Three digital models were created of the slab containing the trackways at Whitby. The first model (Fig. 6) was made from photos taken with the old mobile phone (65 images on a GT-I8190N camera on a 2014 Samsung Galaxy phone). The second model was made from photos taken with a compact SLR camera (81 images on a Canon Powershot SX50 HS 4.3). A third model was made by combining these two sets of data. In all cases, the diffuse and constant light on the specimen from naturally bright but cloudy conditions was ideal.

Fig. 5. The digital 3D model made of the scene with photos taken with the proper Canon digital camera, but with the photographic overlay removed and just showing the morphology of the specimen with angled lighting.

The images were loaded into Agisoft PhotoScan and rendered into 3D models following the workflow in the application: aligning photos, building dense point cloud, building mesh, and building texture. All processes were set to high quality and decimation in the mesh build was avoided by using a custom mesh size set to a high value. PhotoScan performs camera calibration automatically using Brown’s distortion model, but the photos had some EXIF data, which assists the calibration and camera alignment process. The texture file was a jpeg set at 4,096 x 4,096, using Photoscan’s generic texturing method. The finished 3D models were exported from Photoscan as an OBJ file, with associated material and photo-texture file, and uploaded to the online 3D viewing and sharing platform, Sketchfab, for sharing and discussion (see links below).

Clarity of both models was found to be of high quality, showing millimetre scale details of the trackways in the 3D geometry and in the attached texture file. The digital SLR camera would usually produce a better result than the mobile phone camera, because the quality of the optics and resolution of the sensor means it can capture more information. However, the latest cameras in mobile ‘smartphones’ are really very advanced and can make excellent photogrammetry tools. In poor light conditions, they can even produce better results than mid-range SLR digital cameras. They also have the advantage of being much simpler to use.

In the case of the Whitby trackway, photos taken with the old mobile phone produced very nearly as good a result as the digital camera and the model was certainly more than adequate as a record, and for identification and measurement purposes.

In conclusion, capturing multiple images of an otherwise uncollectable object in the field with an old mobile phone camera can enable a scientifically useful 3D digital model to be built to record the specimen and from which measurements can be taken. This data can even be used to 3D-print a displayable solid replica of the fossil, if required. Mobile phone cameras are improving every year so results using this technique are going to get even better.

Fig. 6. The digital 3D model made with 65 photos taken with the mobile phone.

The digital models discussed can be found at these addresses, but they might be slow to open:

The model made from mobile phone photos can viewed here:

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Perhaps unsurprisingly (as a professional dealer in space rocks), I find all meteorites equally fascinating and, in their own way, aesthetically appealing. However, I have to admit, the meteorites known as the Pallasites, with their beautiful structure of olivine fragments suspended in a nickel-iron matrix, are probably the most visually exciting, particularly to the non-specialist. In addition to their undoubted beauty and rarity, Pallasites offer us an intriguing glimpse into the interior of a planet that make them among the most scientifically important of all meteorite types.

The name Pallasite is derived from that of the German naturalist, Simon Peter Pallas. Pallas was one of those amazingly observant and gifted polymaths, who seem to have been a lot more abundant during the eighteenth century, as well as lending his name to a whole class of meteorite, an eagle, a warbler, two species of bat, a wild cat and dozens of other plants and animals.

In 1772, Pallas obtained a 680kg lump of metal that had been found near Kransnojarsk in Siberia. When it was examined in St Petersburg, it was identified as a new type of stony meteorite. In keeping with tradition, it was named after the location where it was found, but, uniquely, the whole class of meteorites was named for Pallas.

There is still some debate about the actual origin of Pallasites. Although some meteorologists contend that the stony-iron structure resulted from a collision between a nickel-iron asteroidal core and a chunk of mantle material (as is the case with mesosiderites), most now believe they originated from the core-mantle boundary layer of differentiated planets that were shattered during vast impacts with other bodies.

That the fifty or so known pallasites derive from a number of such collisions is demonstrated by their chemical and structural differences and by the variation in their ages – from over four and a half billion to just a few hundred million years. (Of course, this reflects the time of the impacts that released them into space.) Additionally, the stony material in mesosiderites is eucritic in nature, indicating an origin on the surface of a planetary body: the olivine crystals in pallasites are so pure that those from the 45 kg Marjalahti meteorite were adopted as the official standard for peridot, the gemological name for crystalline olivine. (Eucrites are meteorites, many of which originate from the surface of the asteroid 4 Vesta.)

Given that Pallasites are beautiful, scientifically important and fascinating relics of planetary collisions, you may be considering adding an example or two to your collection. However, a word of warning. The fate of all polished iron on Earth is to go rusty. Therefore, sliced and polished Pallasites need extreme care to prevent this occurring. The ideal situation would be to display them in a closed cabinet with a dehumidifier. Perhaps surprisingly, these items are not as expensive as you might imagine and can be located quite easily on the Internet. A cheaper solution is to keep your samples in sealed specimen boxes with a silica gel sachet or two. I use the indicating types that change colour to show when they need replacing. Increasingly, meteorite dealers will coat thin polished slices in transparent acrylic to protect them. So long as the pallasite has been thoroughly dehydrated and dried before applying the coat, this process stabilises the meteorite for years.

The two that are most likely to be found in a general meteorite collector’s cabinet are Brahin, which was discovered in 1810, near Minsk in Belarus, and Brenham, originally discovered in Kansas in 1882. Both of these are somewhat prone to deterioration, but display beautiful olivine crystals in a range of colours. In the case of Brenham slices in particular, the crystals are usually in combinations of transparent green, yellow and pale orange.

Undoubtedly the most beautiful (and stable) of all Pallasites are Imilac from Argentina and Esquel, from the driest desert on Earth – the Atacama in Chile. Unfortunately, both are prohibitively expensive, at around £70/gram. A decent slice of either would command a three-figure sum.

Fortunately, there are stable meteorites that are reasonably priced. These are Pallasovka, found in Russia in July, 1990, and Jepara, discovered during the building of a furniture warehouse in Indonesia in 2008. The town of Pallasovka is named after the ubiquitous Peter Pallas, so here we have a Pallasite from Pallas town. The crystals are usually large and brown-orange in colour.

Jepara is an ancient fall in which the nickel-iron matrix has gradually transformed into magnetite, schreibersite and nickel sulphide. Since no further oxidation is possible, Jepara is very stable. Very thin slices display a beautiful structure of greys, silvers and browns, with pale yellow olivines. The limited number of slices I have are further stabilised with opticon and seem to be a really good investment for the private collector.

Other ‘fossil’ Pallasites turn up from time to time. The best-known is Huckitta, found in the Northern Territory in Australia in 1924. Here, the oxidation process is virtually complete, such that the nickel iron has oxidised to silver-grey magnetite and haematite and even the olivine has usually degraded to dark grey crystals. Other similar Pallasites appear on the market from time to time, notably recent northwest African examples (NWA 4482 and NWA 6576). Although lacking the stunning impact of those referred to above, these ancient falls are still fascinating and attractive in their own way. And, of course, they are utterly stable.

No meteorite collection should be without an example of these astonishing and rare meteorites. Now is a good time to take the plunge, but prices will rise dramatically in the very near future as demand outstrips supply. Generally available Pallasites include:

  • Brahin
  • Brenham
  • Pallasovka
  • Esquel
  • Imilac
  • Seymchan
  • Admire
  • Jepara
About the Author

David Bryant has been fascinated by rocks from space since he was a small boy, in large part due to correspondence he enjoyed with Sir Patrick Moore back in the 1950. He is the UK’s only full-time dealer in meteorites and writes and lectures widely about the subject. His website can be found at: www.spacerocksuk.com.

David Bryant (UK)


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Is it possible to find micrometeorites in populated areas? The question has been raised for nearly a century and, despite numerous attempts to find them, the answer up to this day has been a very short “no”. Meanwhile, our knowledge about these amazing stones has gradually increased. There is a continuous evolutionary line in the research on micrometeorites, from the early pioneers, John Murray and Adolf Erik Nordenskiöld in the nineteenth century, to Lucien Rudaux and Harvey H Nininger. With Donald E Brownlee and Michel Maurette in the 1960s, micrometeoritics became real science.

During the past two decades, this research has accelerated thanks to, among others, Susan Taylor, who extracted micrometeorites from the water well at the South Pole, Matthew Genge, who figured out the classification, and other splendid researchers, in addition to the space probes that have returned to Earth with dust samples from comets and asteroids. Today, there is a growing literature about micrometeorites, but still the answer to the initial question is “no” and urban micrometeorites have been considered an urban myth.

Micrometeorites have been found in the Antarctic, but also, to some extent, in prehistoric sediments, remote deserts and in glaciers – places that are clear of the confusing anthropogenic influence. The wall of contamination has been considered insurmountable. It is therefore with pride and joy that I can report here about a project involving the systematic examination of all sorts of anthropogenic and naturally occurring spherules in an empirical search for micrometeorites in populated areas. This research has resulted in a new urban collection of pristine cosmic spherules. The findings have been analysed at several different institutions and, in January 2017, a randomly selected subset of 47 objects from the new collection was prepared for wide beam electron microprobe analysis at the Natural History Museum, London by Dr Matthew Genge (of Imperial College). Nine porphyritic olivine, 23 barred olivine and 15 cryptocrystalline spherules were identified and have textures and mineral compositions identical to Antarctic cosmic spherules. A scientific paper about these new discoveries (Genge et al.) is pending publication, but meanwhile, I can present the results here in Deposits.

The project was initiated in 2009 with a minimum of equipment: a magnet, plastic bags, a sieve and a microscope. To begin with, I sampled accumulated mineral particles from skywards facing hard surfaces like roads, roofs and parking lots in Oslo, and then graduated to look in industrial areas, other cities, countries, mountains, soil, glaciers, beach sand, volcanoes and deserts – that is, everywhere. Now, seven years later, I can look back on nearly with one thousand field searches of about 50 to 5,000µm size particles from nearly 50 countries, all continents represented. The samples were examined in a Zeiss binocular microscope, and interesting particles picked out and photographed with a USB microscope with higher magnification. Promising candidates were analysed using SEM/EDS. I established a photo database (now containing photos of more than 40,000 individual objects) and kept an illustrated journal while I tried to look for patterns. Due to consistently contradictory data in the literature, I put my complete trust in pure empiricism.

Fig. 1. A range of various micrometeorite. (Illustration by Jan Braly Kihle/Jon Larsen.)

To begin with, the various types of anthropogenic and naturally occurring terrestrial spherules seemed infinite and chaotic, but with time, I started to recognise the most common ones. Gradually, I could start the process of systematisation. There are surprisingly small variations in the types of spherules found in comparable environments around the globe. My recently published book, In Search of Stardust, is an atlas of the various types of spherules, and the approximately 30 most common types that represent most of all spherules found anywhere on Earth. In our search for micrometeorites, the knowledge of these contaminants makes it possible for the first time to separate the extra-terrestrial particles from the terrestrial ones. The most recent field searches with improved methodology for processing the samples before the microscopy have given up to one micrometeorite per gram, which is a near match of the Antarctic results.

Cosmic dust belongs to the oldest matter there is: mineral remnants from before the planets were formed. They may even contain real stardust – interstellar particles older than the Sun, that is, particles which have travelled further than anything else on Earth. There is a widespread misconception that micrometeorites are fragments of ordinary meteorites, ablated during their atmospheric flight, but these ablation spherules are not real micrometeorites in the scientific sense. Furthermore, there is a common misunderstanding that micrometeorites are “metal spheres”, but that is only about 2% of them. Most of the cosmic spherules are stony, mainly olivine/orthopyroxene in glass with interstitial magnetite. Their next of kin are the primitive C-chondrites and their origin may lie beyond Pluto. We are just beginning to explore these alien stones, yet they are everywhere around us.

The breakthrough in the search for micrometeorites in populated areas came at last in February 2015, with the discovery of an approximately 0.3mm barred olivine beauty with dendritic magnetite crystals sprinkled over the surface. I started immediately to search for similar stones and found them. At the end of the first season, I had a collection of more than 500 pristine micrometeorites in the size range of between 150 to 600µm, with all the most common types from the classification represented.

For many years, meteorite hunters have built micrometeorite traps of various types. Some have succeeded, like water pools to catch interplanetary dust particles (IDPs), but, given the low influx rate, a really efficient trap would have to be much larger. To catch thousands of cosmic spherules, the trap would have to be the size of a football field (or larger) and accumulate particles over decades. The challenges connected with the construction of something like that have discouraged more than one good scientist. However, there are such areas already in place, possibly in your neighbourhood, and ripe for harvesting: roofs.

The micrometeorites in the new collection were mainly found on the roofs of buildings with a maximum of 50 years of age, so it can be assumed that the stones have a terrestrial age of 0 to 50 years, which make them fresh compared with most of the micrometeorites in the other collections. As a result, some of the surface structures of the micrometeorites in the new collection are different from previous observations, with the glass still intact. With the exception of the Concordia collection from melted snow, most of the Antarctic micrometeorites have a terrestrial age of one thousand to one million years and are weathered accordingly.

By monitoring a skyward facing area like a roof at regular time intervals, it should be possible to be even more precise in future sampling, perhaps down to the week (or even day) that the micrometeorite fell to Earth. With careful preparation (that is, cleaning the collecting area) around the annually reoccurring meteor showers, it should be possible to identify material from some of the comets and possibly also to detect variations in the influx rate over time.

Without knowing what micrometeorites really look like, it would not have been possible to find them, and it is a pleasure also to present here for the very first time micrometeorites in high resolution colour photography. This has become possible thanks to new micro photographic techniques developed especially for this project in co-operation with Dr Jan Braly Kihle. The photo rack was created using a modified Olympus camera together with prototypes and newly invented components (both hardware and software). However, study of the morphological details and textures in high resolution is crucial to understand what to search for in the field samples.

Verifying micrometeorites

One of the returning questions about micrometeorites is how they can be verified. The short answer is: as long as they are chondritic and have the right textures. The definitive evidence for the extra-terrestrial origin of micrometeorites came more than 25 years ago on the basis of noble gas measurements and analysis of cosmogenic nuclei. All particles exposed to the high energy cosmic radiation outside Earth’s magnetosphere are altered, and these changes in the atomic structure can be measured in mass spectrometric analysis. There are also a number of non-isotopic criteria for a positive identification of micrometeorites. First of all, most micrometeorites have a chondritic bulk composition for major and minor elements (at least for particles with a small grain-size relative to particle size), which is easy to check in an EDS analysis. Secondly, the presence of nickel bearing metal in a spherule may suggest an extra-terrestrial origin. However, lack of nickel does not exclude the possibility. It may not be present or the heavier elements may have sunk into a core inside the micrometeorite and is not detectable on the surface. The third main criterion is the presence of a partial or complete rim of magnetite around the micrometeorite. In addition to these three criteria, there are supporting but less definitive features, like high CaO, Cr2O3 olivines and very FeO-poor olivines, which are exceedingly rare in terrestrial rocks.

Until now, little attention has been given to the morphology of micrometeorites. In most reference publications, the stones have been moulded in resin and, therefore, we are presented with black and white SEM section images for study, identification and classification. However, these are poor representations of what the micrometeorites actually look like under the microscope, and the lack of morphological documentation has for a long time caused confusion in the search for micrometeorites in populated areas. Because of the rarity of the micrometeorites up until now, very few meteorite researchers have had access to study real micrometeorites, which is why the precision level about micrometeorites in general is accordingly low outside academic circles. It is my hope that future studies will include documentation of the micrometeorite morphology in the publications and that easy access to these incredible space rocks will result in a new branch of popular meteoritics.

When a micrometeoroid enters the Earth’s atmosphere at a steep angle, it goes through a rapid and unique transformation through melting, differentiation, quenching, recrystallisation and ablation. The result is a stone different from everything else down on Earth. The morphology and the surface textures are characteristic and significant: barred or porphyritic olivine; “turtleback” topography; aerodynamic forms; dendritic magnetite crystals on the surface; a partial magnetite rim; strategically placed metal beads; and so on. In most cases and with experience, a visual identification of a cosmic spherule is unproblematic. When in doubt, a chemical analysis is always recommended.

Origin, formation, influx and classification

There are almost as many explanations as to where the micrometeorites have their origin as there are researchers in the field. Depending on who you ask, the answer may vary from the asteroid belt between Mars and Jupiter, comet related objects in the Kuiper belt or Oort cloud, various planetary ejecta and interstellar matter, to name but a few. It is estimated that up to 0.1% of the matter in primitive meteorites and micrometeorites are presolar grains. On the other hand, there are achondritic (igneous) micrometeorites from differentiated bodies like the Moon and Vesta. Throughout history, large asteroid impacts on the rocky planets and their moons have ejected substantial quantities of rocks into space, and it is possible to imagine an extensive exchange of matter between all the planetary bodies and their surrounding dust rings, with the zodiacal cloud as a temporary storage pool. Hopefully, access to a new, potentially large and renewable source of micrometeorites in populated areas may contribute to a systematic mapping of the isotopic variations of a substantial number of micrometeorites in the years to come, with more data about the micrometeorites parent bodies as a result. It should not come as a surprise if the origins of the micrometeorites turn out to be a combination of all dust producing bodies in the solar system and beyond.

The micrometeoroids enter the Earth’s atmosphere with a speed of up to 50 times that of a rifle bullet. Depending on the entry angle relative to Earth’s rotation, the peak temperature from the frictional heat will cause a substantial variation in the alteration process. Approximately half of the micrometeoroids smaller than 0.1mm receive a soft deceleration and end on the ground as unmelted micrometeorites. The rest reach peak temperatures of between 1,350°C and greater than 2,000°C, which is enough to create the various types of melted cosmic spherules. There are transitional forms between the types, but the chemistry of the micrometeorites is surprisingly homogenous. From the morphology alone, we cannot yet reveal the parent body (origin) of the micrometeorites. A sphere is nature’s solution to maximum volume with the smallest possible surface and is created by the surface tension in a liquid state. At the same time, a rapid differentiation takes place, in which the heavier elements (iron, nickel and so on) move inwards to form a core and volatile elements escape. Iron from the stone reacts with oxygen in the atmosphere and creates dendritic magnetite, looking like small Christmas trees on the surface. Still in flight but decelerating, the inertia of the heavy core may push it forwards in the direction of travel, often spinning. The whole formation is over in the blink of an eye before the micrometeoroids fall to Earth at terminal velocity. Based on radar measurements, the general influx rate of micrometeorites is estimated to approximately one object with a diameter 0.1mm for each square meter every year. This does not sound like much, but adds up to about 100 metric tons a day of mainly micrometeorites like the ones in the photos.

The size distribution of the cosmic spherules has a distinct peak of about 0.3mm, and an object this large contains 27 times more mass than an object with a diameter 0.1mm as described in the influx rate. Consequently, on a roof of 50m2, we cannot expect to find 50 new micrometeorites every year, but rather a statistical possibility of two average cosmic spherules is possible. Future research may add varieties to the present classification, and with more hands and eyes in the field, micrometeoritics can evolve into an exciting new branch of the popular study of space rocks.

About the author

Jon Larsen (1959- ) Norwegian geologist who has studied micrometeorites (MMs) and cosmic dust particles, and published books and articles about these. In 2016 he found a method to retrieve MMs from populated areas, whis had been considered impossible by NASA and other scientific researchers, the discovery was published in Geology (http://geology.gsapubs.org/content/early/2016/12/05/G38352.1.abstract).

During an expedition to search for the first Americal urban micrometeorite (Feb 2017) he found a collection of MMs on the roofs of NASA’s Stardust loboratories. Larsen is afiliated to the University of Oslo (UiO).

This article first appeared in Spacerock Magazine: spacerocksmagazine@gmail.com.

Further reading

The new collection of micrometeorites on Facebook (http://www.facebook.com/micrometeorites)

In Search of Star Dust: Amazing Micro-Meteorites and Their Terrestrial Imposters by Jon Larsen. Published by Voyageur Press, Minneapolis (2017). ISBN: 978-0760352649.

Jon Larsen (Norway)


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Wall games are a very geological form of light entertainment and education. I certainly have amused myself by identifying rocks and their features in walls since my days as an undergraduate and before. I was introduced to the name for the wall game (obvious, I know) by Eric Robinson (1996, 1997). Eric’s examples inspired me to devise my own version of a wall game in far-flung Jamaica. At the time, I was a member of the teaching staff in geology at the University of the West Indies in Mona, Kingston. Each semester, we took the first year classes for three one-day field excursions. As cash was getting ever tighter. I hit upon the money-saving idea of running one of the first trips on campus where there were various ‘urban geological’ features worthy of note. One of these was the stone base of a ruined building that had survived from Mona’s days as a sugar plantation. The rocks in the base were a marvellous mixture of blocks and rounded boulders, presumably collected from the bed of the nearby Hope River, which drains the mountainous country to the east of the university. This trip worked well and, after a few years, the late Trevor Jackson and I published a field guide based on my excursion (Donovan and Jackson, 2000).

The primary criterion for a geologically interesting and educational wall game is a good variety of rocks. The Mona wall game was most satisfactory in this respect, with a mixture of sedimentary and igneous clasts and worked blocks, and even one specimens with a fault running through it (Donovan and Jackson, 2000, fig. 3D-H). But such diverse compendiums of rock types are rare because stone walls have commonly been built from a local source of rock, such as from loose boulders in a river or collected when clearing a field (Anon, 2002). These are commonly composed of one type, that is, the rock that occurs in local outcrop (Nield, 2014). Yet I do not regard this as a problem – rather than searching for different rock types, you can still look for a variety of features shown by one or a few types of local rocks. For example, when on holiday in the White Peak of the Peak District of Derbyshire, I always examine the Carboniferous limestones of the dry stone walls for fossils.

Fig. 1. The wall at the Marriott Worsley Park. Beware that this is a drop-off point and turning circle for cars, so use caution and do not cause an obstruction. Author’s backpack (lower left) for scale.

Sedimentary structures are also an interest if mine, particularly trace fossils in walls (for example, Donovan, 2016, fig. 2H), but also physically- and chemically-controlled structures such as cross-bedding and nodules. This brings me to the Marriott Worsley Park Hotel and Country Club in Manchester. I first stayed in this most comfortable of hotels with my family in 2009 and have been back several times since. The main entrance is down a short slope with a car turning circle, flanked on one side by a slightly sinuous stone wall (Fig. 1). When the site was being rebuilt from its previous (derelict) agricultural origins into a luxury hotel (Redman, 1998), I presume that this wall was built from blocks and boulders already available on the site. In turn, these were likely to have been obtained locally when the original buildings were constructed. It is this wall and its wall game that I want to describe after my most recent visit.

The rocks that outcrop in the area local to Worsley Park are from the Upper Carboniferous (Pennsylvanian) Pennine Coal Measures Group, particularly the Pennine Middle Coal Measures Formation, and the Triassic New Red Sandstone of the Sherwood Sandstone Group, mainly the Chester Pebble Beds Formation (Crofts et al., 2012). The rocks in the Worsley Park wall (Fig. 1) are most probably derived from these units and are mainly Coal Measures. All rocks are siliciclastics, mainly medium- to coarse-grained sandstones, with some pebble conglomerates (Figs. 2 and 3). The principal mineralogy of the blocks is, where the surface is clean enough to see quartzitic (for example, Figs. 2B and 3E). The colours range from pale grey (perhaps ganisters; Tucker, 2011, p. 42) to a straw-brown (Coal Measures) to, less common, a deep purple-red (New Red Sandstone). It is possible that at least some of the latter may include Carboniferous rocks that have been secondarily reddened (Crofts et al., 2012, pl. 3). Although boulders are cemented into the wall with bedding horizontal (such as in Figs. 2D, F, H and I, and 3) to tilted (Fig. 2B and G) to vertical (Fig. 2 A, C and E), I did not see any undoubted cross bedding. In some blocks, the direction of bedding is enhanced by the growth of moss (Fig. 2E). One boulder has a diagenetic development of a haematitic iron pan between bedding planes (for example, Fig. 2A and C).

Fig. 2. Details from the Worsley wall game. All scale bars in centimetres. (A, C) Block mounted with bedding oriented vertically. Bedding is emphasised by a haematitic pan (A), presumably diagenetic in origin. The red colour of the haematite seen in detail on a clean surface in (C). (B) Clean, coarse-grained sandstone. Bedding is dipping gently to the right, as indicated by the particularly coarse-grained bed in the lower half of the block. Note rare pebbles. (D) Block with bedding oriented horizontally. Bedding is emphasised by thin stringers of pebbles that have either dropped out or been eroded out; particularly note the lens-shaped hole left by a presumed large mud clast in the centre. (E) Block with bedding oriented vertically. The direction of bedding is enhanced by the growth of moss along bedding planes. The bedding planes rich in small pebbles are easiest to recognise; note prominent, moderately rounded quartz pebble in centre. (F) Detail of an unusually large mud ‘rip-up’ clast or, at least, the hole where it has been eroded away. (G) Block with bedding dipping to the right. Horizons rich in mud clasts that have largely been eroded away emphasise bedding in the upper half of this block. (H, I) Two lithologically similar slabs of sandstone, both with bedding dipping gently to the left. Bedding is emphasised by the very numerous small pebbles and holes left by pebbles that have dropped out.

Pebbles in conglomerates are either preserved in situ, mainly quartz with some rock fragments (Figs. 2E and 3F), or are mud ‘rip-up’ clasts that have been partially or entirely eroded away, leaving elongate holes in the rock (Figs. 2D, E and G, and 3G). Quartz and lithic pebbles are moderately rounded (Fig. 3F), suggesting that they have a history of fluvial transport. Sand grains are not well-rounded, but angular, indicating that they were not formed in the desert (Figs. 2B and 3E).

One thing of which I am confident is that, although I have spotted some interesting features in this wall, I have not caught them all. In particular, I failed to find any evidence of fossil plants in rocks that I have assumed were mainly derived from the Coal Measures. I invite those in the Manchester area to see both what I have described and to discover what I have not. I shall be back to add to my observations in the not too distant future, I hope. Whatever, this is one of the rare geological sites where I can be confident that there is a comfortable bar and restaurant close at hand in which to relax and reflect on my observations.

Fig. 3. Details from the Worsley wall game. All blocks with bedding horizontal. All scale bars in centimetres. (A) Block with bedding defined by holes produced by the loss of flattened pebbles. (B) Block of red sandstone – either secondarily coloured Coal Measures or New Red Sandstone – with bedding defined by holes left by loss of flattened pebbles, possibly mud ‘rip-up’ clasts. (C) A massive, pale-coloured and quartz-rich sandstone block with poorly-defined bedding. (D) A pale-coloured, quartz-rich sandstone block with well-defined bedding. The bedding is defined by some moderately well-rounded lithic pebbles and stringers of small pebbles. (E) Detail of a quartz-rich sandstone comprised of angular grains. (F) A well-rounded lithic(?) pebble in a sandstone block well covered by mosses. (G) Another mossy sandstone, with numerous holes produced by pebbles, some of which are flattened (presumably mud ‘rip-up’ clasts), which define the bedding. References

Anon. 2002. Dry Stone Walls: The National Collection. Dry Stone Walling Association of Great Britain, Sutton Coldfield, 64 pp.

Crofts, R.G., Hough, E., Humpage, A.J. & Reeves, H.J. 2012. Geology of the Manchester district – a brief explanation of the geological map. Sheet Explanation of the British Geological Survey, 1:50 000 Sheet 85 Manchester (England and Wales): 45 pp.

Donovan, S.K. 2016. Annual meeting of the Geological Society of America, Baltimore, November 2015. Deposits, 46: 9-12.

Donovan, S.K. & Jackson, T.A. 2000. Field guide to the geology of the University of the West Indies campus, Mona. Caribbean Journal of Earth Science, 34 (for 1999): 17-24.

Nield, T. 2014. Underlands: A Journey through Britain’s Lost Landscape. Granta, London, xvii+251 pp.

Redman, N. 1998. A History of the Marriott Worsley Park. Whitbread plc, 26 pp. [Available on-line at http://www.worsleycivictrust.org.]

Robinson, E. 1996. A version of ‘The Wall Game’ in Battersea Park. In Bennett, M.R., Doyle, P., Larwood, J.G. & Prosser, C.D. (eds), Geology on your Doorstep: The role of urban geology in earth heritage conservation: 163-170. Geological Society, London.

Robinson, E. 1997. The stones of the Mile End Road: a geology of Middlemiss country. Proceedings of the Geologists’ Association, 108: 171-176.

Tucker, M.E. 2011. Sedimentary Rocks in the Field: A Practical Guide. Fourth edition.

Wiley-Blackwell, Chichester, xi+276 pp.

Stephen K Donovan (The Netherlands)


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The north of Scotland is famous to scientists and amateur collectors for its wealth of localities where fossil fish of Devonian age can be collected. From plate tectonics, we know that in Devonian times Scotland was situated just below the equator, as part of a continent that was largely arid desert and where land plants were only just emerging. Most life on earth was still aquatic and fishes were the most successful backboned animals.

Fig. 1. The fish beds are found in the Achanarras Fish Bed Member (formerly the Achanarras Limestone Member) and probably mark the Eifelian–Givetian boundary and consist of laminae (that is, very thin strata), which originated as non-glacial varves (annual layers of sediment or sedimentary rock). These were laid down in a lake (Lake Orcadia) during the Middle Devonian.

The fossil fish of the area are unique in many ways. They present a window on the development of vertebrates, in which many of the innovations necessary to pave the way for the next great evolutionary step (the invasion by tetrapods of the land) were already in place. The fauna contains the acanthodians, one of the first group of vertebrates to evolve jaws, and the lobe finned fishes, so called because of their fleshy lobes supporting their pectoral and pelvic fins. The lobe fins also include the lungfish. Their fleshy fin lobes played an important role in the development of the limbs of early four-legged animals (tetrapods) and ultimately to all terrestrial vertebrates today – including ourselves.

The classic Middle Devonian (380 to 375myrs old) locality is Achanarras Quarry in Caithness, where exquisitely preserved fish can be collected in an old roof tile quarry. Many such quarries existed in the past and fish have been widely collected from several localities over the years. The fish are preserved in thinly laminated siltstones and limestones, and this has probably become to be accepted as the normal mode of preservation for the area, whereby the fish died and eventually sank to the bottom of a deep lake in what is known as a lacustrine setting. Fig. 1 illustrates the position of the ancient lake, dubbed the Orcadian Lake (or Lake Orcadie) and shows the deepest part of the lake extended from the tip of the mainland and covered the present day Orkney and Shetland Isles.

Fig. 2. To the east of Thurso, the Ham-Scarfskerry Beds yield a vast amount of fish remains including Asmussia murchisoniana, Thursius macrolepidotus, Dipterus valenciennesia, Homosteus milleri and Dickosteus threiplandi.

The great depth of the lake contributed to the excellent preservation of the fossils, probably due to low oxygen levels on the lakebed and therefore less scavengers and bacterial activity. The fish carcasses lay largely undisturbed in a low energy environment (that is, with an absence of currents) and were gradually covered by river and wind borne influxes of silt and organic matter. These fell through the water column and, over time, were buried at depth in a great thickness of laminated sediment, which is today found as limestones and siltstones. However, the lake was not static and, periodically, the level would rise and fall, depending on the processes that fed water into, and drained it from, the lake.

To the south, the rivers that fed the lake deposited sediments in lowland areas, known as alluvial plains and, during periods of high lake levels, these arid landscapes would be flooded giving rise to semi-permanent, comparatively shallow verges to the lake. This nearshore area we know today as the Moray Firth and here exist equally celebrated fish beds of the same Middle Devonian age, but with a quite different process and mode of fossil preservation.

‘Nodule’ bed localities

The nearshore environment was rich in calcium carbonate, probably derived from the mineral rich sediments of the underlying alluvial plain, and gave rise to a form of preservation commonly known as nodules. These are round to oval, sometimes flat or irregular, smooth shaped carbonate clasts, which can vary in size from around 5mm to 600mm. Note that the term ‘nodule’ is technically incorrect, as this type of preservation is accurately called a concretion. However, over time, these two terms have become interchangeable when discussing the Scottish localities and therefore ‘nodule’ will be retained for the purposes of this article.

The Achanarras fauna

It is estimated that 18 or 19 species of fossil fish and a single arthropod make up the Achanarras fauna throughout the Achanarras horizon. Recent discoveries have augmented this number from a previous figure of around 14 to 16. The fish forms represented are;

  • Acanthodians or ‘spiny sharks’.
  • Agnathans or jawless fish.
  • Ray fins.
Fish preserved in nodules

Whereas today’s collector would usually expect to gather specimens in the classic fine grey flagstone matrix typical of the northern quarries, the Moray Firth localities still yield nodules and some of them contain the fossilised remains of fishes. However, most nodules do not contain remains and considerable investment of time is required to collect a single fish-bearing nodule. The reason is that, like Achanarras Quarry, the fish are preserved only at certain levels within the nodule bearing outcrop, where the nodules occur in both limestones and relatively soft clays. Collecting from the outcrop is prohibited by the Scottish Fossil Code. However, collecting from talus, shingle and stream beds is allowed and, in these instances, both barren and fish bearing nodules derived from the full thickness of the outcrops are mixed together, with few differentiating features. Therefore, every nodule found should be investigated onsite to determine whether it has potential.

Fig. 3. Complete fish at Achanarras are now rare, but can still occasionally be found. Fig. 4. Coccosteus head shield from the Devonian, Achanarras, Scotland Preservation mode

In the Orcadian Lake, preservation in concretions (nodules) occurred in shallow water near the lake margin, when the lake was at its deepest and transgressed the alluvial plain environment.

Fish preserved in nodules can be more disarticulated and incomplete compared to those preserved in deep lake siltstones and limestones, and individual spines, scales or dermal plates may be all that is preserved within the nodule. This is perhaps due to a greater abundance of scavengers and nearshore currents. However, such specimens can be equally valuable scientifically, as some features can be more clearly exposed.

The chemistry involved in the formation of concretions enclosing fossils is not fully understood and appears to vary considerably, and laboratory experiments have so far failed to reproduce concretion formation (McCoy, 2013). Preservation also varies from the spectacular 3D preservation of the occupant, for example, in the Santana Formation in Brazil, to the situation seen in Scottish deposits, where the fish is completely compressed.

An abundance of calcium carbonate is required for the calcareous nodules to form and this, to an extent, may be derived from mineral rich sediments (caliche) within the transgressed alluvial plains. It is perhaps augmented by carbonate deposition by lake margin plants (Gierlowski-Kordesch, 2010) and concentrated by evaporation. Fish would die and sink to the lakebed where, presumably, burial would be more rapid due to the proximity of sediment supply from the rivers that fed the lake. While still in the soft sediment phase and shortly after burial, it is presumed that carbonate ions, in solution, migrate towards the carcasses, cementing the grains of sediment and forming a jacket around the fish. Once buried at great depth, the sediment is compacted and lithified, and the nodules generally become harder than the surrounding sediment. It has often been reported that nodules containing fish are fish shaped. In Lake Orcadie deposits, the nodules tend to be round to oval, except in specific deposits, for example, Tynet Burn Upper Nodule Bed, in the bottom and middle units.

Fig. 5. Larger fragments of fish bone and head shields are extremly common from Thurso.

The size range of, and preservation within, these nodules can vary greatly. At Tynet Burn, pea-sized nodules can contain a single fish scale, while at Edderton, nodules weighing many kilos can enclose several fish. The figure demonstrates the unique preservation mode and nodule formation and disruption. This is typical of Tynet Burn nodules, where deformation of the soft sediment during water release events, followed by localised tectonic events, resulted in the nodules being broken and re-cemented by carbonate infilling.

As previously stated, the bulk of all nodules are barren and this means that the reason for their formation seems more difficult to explain, there effectively being no nucleus present. However, one reason may be that formation commenced around a mineralised event or that the decomposition process continued after the nodule formed, eventually leaving no trace of the original carcass.

My colleagues from Aberdeen University and I have excavated all the known nodule localities with the permission of both the landowners and Scottish Natural Heritage, and this work has shed light on questions surrounding the apparent different types of nodules, as illustrated in Fig. 3. It can be seen that the preservation at Edderton, Eathie/Cromarty and Gamrie comprises dark bone on a grey matrix, similar to that observed in the deep water siltstones. On the other hand, the nodules from Tynet Burn and Lethen Bar appear quite different. They are unusual in that the fish are preserved in crimson and purple colours and, over the years, this has rendered these specimens very desirable to collectors. This type of colouration is typical of iron compounds, but why would these localities yield fossil bone preserved in this way?

Fig. 6. The rocks at Thurso are full of scales, which can easily be collected.

The answer was realised during examination of Tynet nodules under the microscope, when thin sections revealed microscopic remains of fossilised filamentous bacteria in calcite. It became clear that, after burial, these anaerobic forms of bacteria were processing the fish carcasses by metabolising the naturally occurring iron in the organs and tissues with the by-product iron oxide being deposited, thereby giving the fossils their unique and exquisite colours. Furthermore, at sites within the carcass where iron was concentrated in blood rich organs (the kidneys, liver and heart), a higher concentration of deposited iron oxide reveals the position of these organs in rare cases.

Collecting today

Because of their unique attraction, all the sites have been stripped over the last 150 years and yield little or no loose material today. Fossils can still be found in nodules in shingle at Cromarty and Eathie, and responsible collecting is encouraged by information boards there. However, all of the localities are sites of special scientific interest (SSSI) and special access permission is also required at Tynet Burn, Gamrie and Edderton. The Lethen Bar site was worked commercially for lime in the nineteenth century and its exact location is not currently known. The Tynet Burn site is now completely overgrown and requires excavation to yield more material or to examine the outcrop. However, excavation of the outcrops is not allowed at any locality without robust scientific justification.

 Bob Davidson(UK)

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I grew up in the 1940s and 50s in the eastern US state of Maryland and went to cinemas on my own from the age of six, mostly to see what were then to me exciting western movies. In 1962, I was off to graduate school in the Great Plains state of Nebraska, a place that I pictured in my mind as it had been depicted in some of those films. Imagine my surprise when it looked nothing like the outdoor scenes in most of those films. Silly me, to have thought that films were made as closely as possible to the real subject area.

From graduate school in 1962 to now, I achieved my goals and became a geologist and professor, travelling and doing research in the Great Plains and western Central Lowland physiographic provinces, and looking at geology in exotic places like the UK, China, Australia and New Zealand. Fast forward to 2013. I had enough experience and expertise on Great Plains geology by then that I was asked to write a short book of about 35,000 words on the geology of the Great Plains by the director of the Center for Great Plains Studies at the University of Nebraska, Dr Richard Edwards. After visiting and studying sites in Alberta and Saskatchewan in Canada, and in south-western Texas that I had not previously studied, I started working on the book now titled Great Plains Geology that is reviewed in this issue of Deposits on the page opposite (Fig. 1).

Fig. 1. John Wesley Powell’s coloured map of the US physiographic provinces (1895). The area shaded in a deeper blue just to the left of centre is Powell’s Great Plains.

I may be wrong, but I think that few people from the UK have much of a mental image of the Great Plains or know its boundaries. Certainly, that is true of most of our citizens in the USA. The area of land included in the Great Plains has been much debated since the late 1800s, when the physiographic region was defined and its area probably drawn for the first time on a map by the second director of the US Geological Survey, John Wesley Powell (Fig. 2; 1895). Powell only included the part of the Great Plains in the US on his map, but wrote that the place extended north into the Canadian prairie provinces of Alberta and Saskatchewan, and south into a small part of northern Mexico. I have included descriptions of some sites in those areas of the Great Plains in my book.

Readers of Deposits have a background in the jargon of geology and palaeontology, so I do not need to spend time defining too many terms. Instead, let me tell you that much of the Great Plains is beautiful and that most of the people are friendly. The place has spots that are spectacular ecotourism sites where, if you plan ahead and are lucky like my wife, Anne, and I, you can see wildlife, such as bison, moose and coyotes (Figs. 3 to 5), and migrations of vast flocks of geese, ducks, white pelicans, Sandhill cranes and other wonderful birds.

Fig. 2. Bison grazing in western South Dakota. (Photo by Anne Diffendal.)

Much of the Great Plains is semiarid: that is, it receives on average less than 50cm of precipitation a year, although along the eastern border, there is somewhat more on average. Precipitation from year to year and from one part of the region to another year to year can vary greatly. Temperatures also vary greatly during the year and even during the day. Visitors or residents need to watch weather forecasts and radar regularly every day, and to look for changing weather conditions when in the countryside.

As you travel across the Great Plains, you can observe and interpret many geological features. One feature is easy to interpret if you know what to look for in the landscape. There are many places on the Great Plains where buttes and mesas are capped by gravelly river deposits. These mark the former low spots on the landscape, now high and dry because the rivers and streams that carried them to those places have shifted courses and eroded much more deeply into the adjacent more easily eroded, finer-grained sedimentary strata. This left an inverted topography with the river deposits high above those now accumulating on the floors of the new valleys. The Cypress Hills of south-eastern Alberta and south-western Saskatchewan in Canada, and Castle Rock, Colorado in the US are two such places described in my book (Figs. 6 to 8). Even though the capping river deposits are discontinuous, sometimes unusual rocks in them were eroded from narrowly confined outcroppings of rocks in distant uplands, so at least parts of former drainage systems can be traced out. This form of comparison and matching of rock types to work out former drainage paths has been applied by geologists successfully since at least the late 1800s. In the case of the Cypress Hills, researchers studying the gravel types have linked them to erosion from the Sweet Grass Hills, a small, isolated mountain area with about 900m of relief located about 80km to the southwest in the state of Montana. On the other hand, the cemented gravels at Castle Rock contain large pieces of volcanic tuff eroded from outcrops of that rock along the valley side of the ancient valley, as well as key rocks transported from more distant places in the adjacent Southern Rocky Mountains.

Fig. 3. Coyote in western South Dakota. (Photo by Anne Diffendal.)

I included outstanding Great Plains archaeological and paleontological sites in addition to or combined with ecotourism and geologic features sites in my book. Head-Smashed-In Buffalo Jump in southern Alberta in Canada, located about 194km south of the Calgary airport, is one such place. This spectacular UNESCO World Heritage Site, so designated in 1981, is on the east-facing side of the Porcupine Hills, near the southern end of these hills and adjacent to the Old Man River. The jump site is due to exposed thick river-deposited sandstone beds that form a discontinuous escarpment near the top of the hills (Fig. 9) over which Native Americans drove bison to their deaths at many times over at least the last 5,700 years. Anne and I first visited this site decades ago with our Canadian friends from Alberta, John and Karen Hillerud. Since then, the visitor centre, built into the hillside, has been greatly improved and now has outstanding interpretive displays that explain the archaeology, geology and other features of the site. There is a wonderful replica of the cliff with bison poised to race off of it and of the archaeological dig site below (Fig. 9).

Three paleontological sites in the US – Hot Springs Mammoth Site, Agate Fossil Beds National Monument and Ashfall State Historical Park – ought also to stimulate your interest in visiting the Great Plains. Hot Springs Mammoth Site is located in the city of Hot Springs in South Dakota, slightly more than 100km south of the Rapid City, South Dakota airport. In 1974, a contractor was having the site cleared for a development when his crew bladed off parts of a mammoth skeleton and stopped work to assess the situation. My colleague, Dr Larry Agenbroad, was asked shortly thereafter to take a look at the site and found more bones. Larry, and his students and colleagues, mapped out the area where the bones occurred. Over the years since 1974, the site has been preserved and greatly improved with the still-being-worked excavation site enclosed now in a very nice visitor centre.

Fig. 4. Moose munching water plants in south-western Alberta, Canada. (Photo by Anne Diffendal.)

The mammoth skeletons (Fig. 10) and those of many other species of fossil animals died about 26,000 years ago and are preserved in ancient, thinly-bedded sinkhole deposits. These are surrounded on all sides by red, clay-rich Permo-Triassic beds. The sinkhole must have been filled with water in the Late Pleistocene and was a natural trap for unwary animals because of its steep and slippery clay sides. Most of the mammoth skeletons found so far are reportedly of young males. Make of that what you will, but that is interesting.

Fig. 5. Castle Rock, Colorado. (Photo by author.)

The fossils at what is now Agate Fossil Beds National Monument were discovered in 1885 by James Cook and his soon-to-be wife, Kate, on conical buttes (Fig. 11) near a ranch house on a ranch along the side of the Niobrara River in western Nebraska that would soon be theirs. Over the years since then, palaeontologists from many famous universities, such as Yale University, the University of Nebraska and Carnegie University, have excavated fossils there. My friend, Dr Bob Hunt, Professor Emeritus of the University of Nebraska and his students and colleagues, have done most of the recent major work there and at adjacent parts of Sioux County in Nebraska.

Fig. 6. Conglomerate on the top of the Cypress Hills, West Block, Alberta, Canada. (Photo by author.)

The Early Miocene fossils found at Agate include: small rhinos; camels; horses; corkscrew-shaped burrows and the skeletons of fossil beavers that dug them; species of an extinct lineage of herbivores called oreodonts; chalicotheres (animals that looked like a big horse with clawed feet); entelodonts (the so-called “giant hogs” that filled the omnivore/scavenger niche); and amphicyonids or bear-dogs. What a wild and crazy menagerie that must have been.

When I first went to the park in the 1960s, the only roads to there were unpaved and the one from Mitchell to Harrison in Nebraska, had signs up saying “No Services for the next 60 miles” (about 100km). Today, that road is paved to the turnoff to the National Monument but that sign has stayed the same. Gas up before you visit.

Fig. 7. Conglomerate with large, light gray tuff clast, Castle Rock, Colorado. (Photo by author.)

Ashfall Fossil Beds State Historical Park is located on the extreme eastern side of the Great Plains in Antelope County, Nebraska, just a few miles west of the former western margin of the Early Pleistocene ice sheets. The site was discovered in 1971 by my long-time friend and colleague, Dr Mike Voorhies, while he was searching for fossils near his home.

In Late Miocene times, the largely river deposits of the Ash Hollow Formation there were laid down on the floodplains of rivers shaded by trees. The ground in the valleys was irregular and small ponds formed in low, poorly drained spots. Many animals were drawn to these water sources. A supervolcano erupted on what is now the Snake River Plain in the state of Idaho, some 1,600km to the west of the park site about 11.93mya. Volcanic ash from that eruption was carried to the east and rained down on the land from the volcano eastward at least onto the park site, leaving behind correlative ash deposits in low protected spots like the former pond. The ash at the park is up to three metres thick and contains many fully articulated skeletons of such animals as rhinos (Fig. 12), several genera and species of three-toed horses, camels, primitive deer, carnivores, rodents, a snake and a giant land tortoise. Also recovered are skeletons of a bird similar to a secretary bird, crowned cranes and an eagle-like vulture.

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The sorry tale of Johann Beringer has been part of the folklore of palaeontology for almost 200 years. In 1726, Beringer published a book illustrating some extraordinary ‘fossils’ reputedly found in the rocks close to Würzburg in southern Germany. However, very soon after its publication, Beringer realised that he had been tricked and that the specimens were fakes. The truth about the deception – and its perpetrators – is still shrouded in mystery, and the story of Beringer’s Lügensteine (’lying-stones’) ranks with Piltdown Man as the greatest of all fossil frauds.

Who was Beringer?

No portrait exists of Johann Bartholomew Adam Beringer (1667–1740) despite the fact that he was an important figure in Würzburg during the early eighteenth century. The son of an academic, Beringer became Chief Physician to the Prince Bishop of Würzburg and Duke of Franconia (Christoph Franz von Hutten) and to the Julian Hospital, and was also the Dean of the Faculty of Medicine at Würzburg University. Like other learned men of the time, Beringer kept a ‘cabinet of curiosities’ said to contain ammonites, belemnites and sharks’ teeth. He seems to have led a conventional life for someone of his high standing until May 1725, when an unfortunate train of events was set in motion. Three young men employed by Beringer to supply him with fossils delivered the first of a truly remarkable series of specimens purported to have been found at Mount Eibelstadt, a few kilometres south of Würzburg. These are the infamous Lügensteine, or iconoliths, described by Beringer in the Lithographiae Wirceburgensis of 1726. The original text was published in Latin, but Jahn and Woolf (1963) have published an excellent English translation accompanied by scholarly background information. Lithographiae Wirceburgensis contains 21 plates, depicting 204 specimens. A typical example is reproduced in Fig. 1.

Fig. 1. Iconoliths of insects. Plate 16 of Beringer’s Lithographiae Wirceburgensis (1726). The Lügensteine

Rocks of the Middle Triassic Muschelkalk (‘shell limestone’) outcrop at Eibelstadt and can be seen in the soil of the vineyards that carpet the region today. The Muschelkalk contains abundant fossils of marine animals, including ceratitid ammonoids and bivalves, but Beringer’s iconoliths were something entirely different. Indeed, Beringer himself made it clear in his book that they were not ordinary fossils. Although there are a few iconoliths that superficially resemble true Muschelkalk fossils, even these are decidedly peculiar on closer inspection. For example, one specimen seems to be a ceratitid on one side, with a characteristic lobe and saddle suture pattern, but the imbricated radial markings on the other side are utterly different and quite unlike anything known in this group of ammonoids (Fig. 2).

The remaining iconoliths range from the barely credible to the totally incredible (Figs 3 to 11). The bulk of Beringer’s iconoliths are bas-reliefs, in which the ‘fossil’ fits almost exactly the shape of the rock, something which Beringer himself remarked on in his book: “The figures expressed on these stones, especially those of insects, are so exactly fitted to the dimensions of the stones, that one would swear that they are the work of a very meticulous sculptor.” (Jahn and Woolf, 1963, p. 35). A few iconoliths take the form of moulds (that is, negative impressions), but most are in positive relief. Preservation is invariably perfect and the animals and plants are complete – for example, the plants may have roots, stems, leaves and flowers (Fig. 3). All of the animals and plants are in ideal orientations for their anatomical features to be observed clearly. There is no compression or other distortion.

While some of the ‘iconoliths’ display animals with shells or skeletons, the majority are soft-bodied organisms. In the few iconoliths of shell-bearing animals, there is no distinct shell, just its shape in the limestone. A few examples exist of vertebrates with bony skeletons, but these are anatomically incorrect. For example, a bird iconolith (Fig. 4) has absurdly coarse ribs. Other birds are preserved next to clutches of their eggs. Rarely, two different ‘fossils’ occur on opposite faces of a single iconolith (Fig. 5).

Apparent examples of predators caught in the act of capturing their prey are common (Fig. 6), as are animals mating, especially frogs (Fig. 7). There are several examples of incongruous assemblages of fishes, moths, snails and so on, on a single iconolith (Fig. 8). It is worth noting that few, if any, of the organisms can be precisely identified – for many, the broad taxonomic group is clear (for example, frogs and beetles), but, for others, even this is difficult to ascertain. Featureless elongate forms may represent either worms or snakes. There are a few mermaid- and angel-like iconoliths (Fig. 9). Vying with these for the honour of being the most bizarre are iconoliths shaped like miniature celestial bodies – the sun, moon, stars and comets (Fig. 10) – and others representing Hebrew script (Fig. 11). It is worth noting that, in the early eighteenth century, the possibility of fossils taking the shape of celestial bodies and somehow related to objects seen in the sky was not considered to be preposterous. Witness the pentaradiate stem segments of isocrinid crinoid fossils, widely known as ‘starstones’.

The sheer scale of the fraud is astonishing. It is estimated that over 1,000 iconoliths were manufactured, all probably made within the space of about a year. More than 490 iconoliths survive today in various European museums (Niebuhr and Geyer, 2005). The greatest numbers are in the collections of the University of Würzburg and the Mainfränkisches Museum in Würzburg, with a combined total of 311 specimens, and the Oxford University Museum owns two examples (Edmonds and Powell, 1974). The Muschelkalk limestone in which they are carved is a compact and well-lithified micrite, demanding physical effort to work. It is possible to envisage a cottage industry of stone cravers labouring energetically in the period leading up to the publication of Beringer’s book.

Fig. 12. The frontispiece of Beringer’s Lithographiae Wirceburgensis (1726). Whodunit?

As for the ‘whodunit’ element of this fraud, a popular myth is that Beringer’s students carved the iconoliths as a prank. Only when Beringer discovered an iconolith carved with his own name did he realise he had been fooled. This is the story told, for instance, in a standard early book on the history of geology and palaeontology written by Karl von Zittel (1901, p. 18). However, evidence from court records (see Jahn and Woolf, 1963) suggests instead that the culprits may have been two of Beringer’s colleagues at Würzburg University. Within days of the publication of Lithographiae Wirceburgensis, Beringer initiated a judicial enquiry against the three collectors from Eibelstadt, who in turn implicated J Ignatz Roderick and Georg von Eckhart, respectively Professor of Geography and Algebra and librarian. Unfortunately, the final outcome of the enquiry is unknown as the records are incomplete. It has even been suggested (Niebuhr and Geyer, 2005) that Beringer himself may not have been an entirely innocent party in the fraud.

Fig. 13. Some of the products of the Lügensteine Association. Beringer in context

It is all too easy with our modern knowledge of fossils and how they are formed to dismiss Beringer as a gullible fool. In the early eighteenth century, however, the true origin of fossils had not been completely established and there was a poor understanding of what could and what could not be fossilised. Granted, Steno and others before him argued convincingly that fossils were the remains of once living organisms naturally entombed in sediment, but various alternative theories of fossilisation were still being debated. These included vis-plastica, whereby fossils grew inorganically in the rock like minerals, and the Spermatick Principle, explaining at least some fossils as the progeny of the airborne seeds of marine animals that became lodged in cracks in the rocks and developed into fossil shells resembling, though not identical to, animals living in modern seas. Beringer’s book tried to apply these and other theories of fossilisation, such as the Biblical Flood, to his iconoliths, but he was unable to reach any firm conclusion. Paradoxically, given his change of opinion after the book was published, he went to great lengths explaining why they were not of human manufacture, despite the fact that several had apparent scratch marks on their surfaces as if made by a knife. Beringer acknowledged that some fake iconoliths had been produced and he even witnessed one being carved. These he considered to be like fake Roman coins made by the unscrupulous to profit from the high value of the genuine articles. However, he claimed that he could easily distinguish the fake from the real iconoliths.

Why did Beringer cling to his belief that the iconoliths were natural objects and what made him eventually change his mind? These are difficult questions to answer. Beringer wrote that he had been favoured by Divine Providence to have the iconoliths delivered to him for description, which may have pre-empted any questioning of their authenticity. One school of thought (Cooper, 2007) is that he was motivated by the desire to glorify Franconia, the unique presence of the iconoliths raising the stature of Franconia above neighbouring regions. The elaborate frontispiece of Lithographiae Wirceburgensis depicts several classically dressed figures deporting themselves over a hillside littered with iconoliths and capped by a monument bearing the emblem of the Prince Bishop of Würzburg (Fig. 12). Together with the book’s dedication, this makes it clear that Lithographiae Wirceburgensis was aimed at the head of state of Franconia, Prince Bishop Christoph Franz von Hutten. Ironically, it may well have been von Hutten who finally persuaded Beringer that he had been cruelly deceived.

Fig. 14. Mating frogs key ring from the Lügensteine Association. Lügensteine renaissance

Beringer’s iconoliths became the talk of polite German society immediately after the fraud was revealed. Except for a few articles (for example, Taylor, 2004; Pain, 2004; Pain and Byrd, 2005) and, unlike the Piltdown conspiracy which still attracts considerable public interest, Beringer’s Lügensteine have been relatively neglected. However, there is now a Lügensteine Association in Germany, with a small museum and web pages devoted to this fascinating case of fossil fakery on a massive scale (https://www.beringers-luegensteine.com/en/home.html). The aim of this association is to encourage research on the Beringer fraud. To publicise its activities, the association produces replica Lügensteine, some as chocolates, soap or key rings (Figs. 13 and 14). Now there’s something not yet tried for Piltdown Man.

About the author

Paul Taylor is a Merit Research Scientist in the Department of Earth Sciences, Natural History Museum, London.

References

Beringer, J. B. A. 1726 Lithographiae Wirceburgensis. Würzburg: Fuggart.

Cooper, A. 2007 Inventing the Indigenous. Cambridge: Cambridge University Press.

Edmonds, J. M. & Powell, H.P. 1974 Beringer ‘Lügensteine’ at Oxford. Proceedings of the Geologists’ Association 85: 549–554.

Jahn, M. E. & Woolf, D. J. 1963 The Lying Stones of Dr. Johann Bartholemew Adam Beringer being his Lithographiae Wirceburgensis. Berkeley and Los Angeles: University of California Press.

Niebuhr, B. & Geyer, G. 2005 Beringers Lügensteine: 493 Corpora Delicti zwischen Dichtung und Wahrheit. Beringeria Sonderheft 5(2): 1–188.

Pain, S. 2004 Johann and the magic stones. New Scientist, 25 December 2004/1 January 2005: 74–75.

Pain, S. & Byrd, B. 2005 Johann and the Magic Stones. Muse 9(5): 38–43.

Taylor, P. D. 2004 Beringer’s iconoliths: palaeontological fraud in the early 18th century. The Linnean 20: 21–31.

Zittel, K. A. von 1901 History of geology and palaeontology. London: Scott.

Paul D Taylor (UK)


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Agate is banded or variegated chalcedony and this distinctive appearance allows a ready identification from any source. Many agate thick sections from basic igneous hosts are reminiscent of a series of distorted onion-like rings with the initial bands closely replicating the shape of the supporting gas cavity. However, the banding is frequently distorted and this general pattern is known under various names, for example, fortification or wall lining. A second type is less common and demonstrates apparently gravity-controlled horizontal bands. Agate host rocks are varied but the most abundant agate sources are the gas cavities of basic igneous rocks. This article limits discussion to agates from these basic hosts. However, agates can also be found in some igneous acidic hosts (for example, rhyolite), sedimentary rocks (for example, limestone) and in some fossils.

Agate is greater than 97% silica (SiO2) and shows little variation between different samples. Under normal earth surface conditions, silica occurs in a number of forms. It is most commonly found as alpha-quartz and this is the major component in agate. A second silica constituent is moganite with a concentration at 2 to 25%. Moganite is found in agate that has not been heated by metamorphism or in the laboratory. Together with alpha-quartz, they are usually the only forms of silica identified in agate. However, other forms of silica such as cristobalite and tridymite have been occasionally identified in agate. In agates from basic igneous hosts, calcite is a rarity, as demonstrated by an examination of 180 worldwide agates using powder X ray diffraction. Trace calcite was identified in just 7 agates and 4 came from one source – Las Choyas, Mexico (Moxon unpublished data). The major non-volatile impurities include iron, aluminium, magnesium and sodium but concentrations are very small and measured in parts per million; collectively the total is much less than 1% (Götze, 2001). Surprisingly, water (up to 2%) is the major agate impurity. However, only a fraction of the water is due to actual water molecules (H2O). The bulk of detected water is obtained through water loss from two neighbouring silanol groups (≡Si—OH).

Agate/chalcedony has been found in host rocks as young as 13 millions years (Ma) and as old as 3,720 Ma (Moxon et al., 2006). However, agate has never been made in the laboratory. It develops during ageing and these changes allow valid speculation about agate in its early years. This article considers the essential role that water and moganite play in these age-related changes. Mineral age-related development is rare but it is not unique to agate. One other example showing ageing changes is bone apatite. The change offers a means of approximately dating ancient bones (Bartsiokas and Middleton, 1992).

Relationship between agate and host rock age

Agates could form around the same geological time as the host or hundreds of millions years later. Hence, the relative timing of host and agate formation is a prerequisite before any attempt can be made to link agate and host rock age. Many agate host rocks have been dated using radioactive isotopes. Unfortunately, the agates themselves have not been dated due to either a limited radioactive isotope content and/or costs. Agate/chalcedony from the Yucca Mt., Nevada, USA is an exception and has been radiometrically dated together with the host. Yucca Mt., aged 13 Ma, was under consideration as a potential nuclear waste repository and investigated for more than 30 years. The intended nuclear storage has resulted in many studies examining water flow including its effect on the Yucca Mt. host rock minerals. One of these studies dated the chalcedony that had formed in Yucca Mt. tuffs. Initial chalcedony coatings appeared around 4 Ma after the host formation (Neymark et al, 2002). However, radioactive isotopes are generally limited in agate and published agate/chalcedony dating, as far as I am aware, is limited to this one example.

Alternative methods are required and agate properties do vary from source to source offering the opportunity to test potential links with the host rock age. Once a property has been identified, it needs to be investigated with respect to the known host rock age. A plot of any quantitative data against host rock age will produce either random values and is therefore of no use for dating purposes, or show trends with respect to the age of the host rock. If trends can be identified, then that particular property potentially provides a method of roughly dating the approximate agate age. Over the years, I have looked at a variety of property changes and found some that produce a host age link. Quartz crystallite size, density, moganite and total water content do show either partial or total connections with the host rock age. A number of agates need to be examined from a particular area but at best, the sample mean values show a variation range of 5 to 15% and none match the precision of radiometric dating.

Quartz crystallite size. Most minerals are crystalline: they have a definite form due to the long-range order of component atoms or ions. Even complete crystals in macrocrystalline quartz are composed of many smaller crystal units known as crystallites. Crystallites are measured in nanometres (1 nm = 10-9 m) and the crystallite size can be determined using powder X-ray diffraction (XRD). X-rays are part of the electromagnetic spectrum that has a decreasing wavelength when passing from infrared à visible lightà ultraviolet à X-rays. For XRD, a diffractometer generates and directs X-rays at finely ground crystalline powders and the resulting diffraction and interference effects are recorded electronically. The X-ray angle of incidence is measured in degrees theta but the collected data adds the angle of reflection and is recorded as 2 theta. Each pattern of peak positions is as diagnostic of a particular mineral as are human fingerprints. An amorphous (non-crystalline) substance such as glass or plastic is without peaks and shows as a single broad hump. The collection of peaks (Fig.1) are unique to α-quartz and the agate samples are from (a) Mt. Warning, Australia (23 Ma, host age); (b) Chihuahua, Mexico (38 Ma); (c) Lake Superior, USA (1,100 Ma). All show the same peaks that are given by Brazilian macrocrystalline quartz (d). The largest signal intensity is around 26o 2 theta. This is approximately five times greater than the second largest signal at around 20o 2 theta and 10 to 20 times greater than the remainder. A plot using full intensity would result in these two main peaks minimising the rest. Square root of signal intensity reduces this effect. Points of interest are:

1) Agate shows the same signal positions as the Brazilian macrocrystalline quartz.

2) The signals become narrower from (a) to (b) to (c) to (d). The narrower signals demonstrate an increasing crystallite size.

3) These XRD scans have used a fairly rapid time scan. A slower scan would reveal moganite in all the agate samples. However, the moganite signal (m) still shows its presence in the younger agates.

Moganite is the most recently discovered form of silica having been identified in 1984 and finally accepted as a new mineral in 1999. Detection of moganite in agate is usually done using powder XRD. However, moganite quantification can be difficult at low concentrations as it is widely distributed and makes a limited contribution to the moganite XRD signals. Raman spectroscopy is more sensitive and readily identifies trace moganite that has been detected in agate from hosts as old as 1,100 Ma. Visual evidence of this identified development will be considered next.

Scanning electron microscope (SEM)

Optical microscopes are limited to a magnification of about 1,000 x and a thin section examination of agates from hosts aged between 30 Ma and 1,100 Ma does not produce any observable age-related changes. Electron microscopes use accelerated electrons in place of light and the SEM has an increased magnification up to around 500,000 times. The SEM can be used to examine a fractured agate surface that has been coated in a conducting material such as gold or carbon. Early SEM work on fractured agate identified globules in the non-white areas (Lange et al., 1984). Further work distinguished differences between the white bands and the non-white area. The white bands in the older agates were described as showing a stacked plate-edge like structure while the globular structure showed a general age-related increase in size (Moxon, 2002). There is a common trend with an increasing age-related globular growth but differences are not readily quantifiable because there are variations in globular size within the same agate.

Fig. 1. X-ray diffraction signals produced by agates from: a) Mt. Warning, Australia (23 Ma host rock age); (b) Chihuahua, Mexico (38 Ma); (c) Lake Superior, USA (1,100 Ma). All show the same signals that are given by the Brazilian macrocrystalline quartz d). A weak moganite signal (m) is shown in two of the agate samples (a) and (b). The square root of reflection intensity has been used in all cases; silicon (Si) is added as an internal standard.

Relationships between different features are lost at high SEM magnifications and one examination routine is shown by the link between increasing size and detail in the Lake Superior agate (Fig. 2, I à IV). Here, the globular nature of the clear area (a) contrasts with a fine white band (b). This band is very unusual, the normal plate-like structure is not observed and it appears to be a collective infill of broken fragments. Further structural detail is demonstrated by taking enlargements around the centre producing the Fig. 2 micrographs. Much of the observed surface debris is caused by the preparation. However, the higher magnification shown in Fig. 2 (IV) does allow an observation of genuine globular growths that have also developed on the white band at (e). The micrograph in Fig. 3 shows a white band that is well formed and typical of that found in agates older than about 60 Ma. The bottom edge of the micrograph (c) shows the repeated vertical stacking of the plate-like edges. Occasional twists of the “plates” have produced flat surfaces (d).

The white band differences between young and old agates can often be demonstrated without the use of the SEM. In my experience, agates from younger hosts (for example, Mt Warning Australia (23 Ma); Isle of Rum, Scotland (60 Ma); Woolshed Creek, New Zealand (89 Ma); Rio Grande do Sul, Brazil (135 Ma) show white bands that are less intense and often more diffuse than those from older agates such as those from Botswana (180 Ma) or Lake Superior (1,100 Ma). If a lapidary diamond saw is available, then an age-related judgement can be made. The agate slabs in Fig. 4 I and II, both 2mm thick, are respectively from Botswana (180 Ma host age) and New Zealand (89 Ma). When viewed against strong white light, the white bands in the older agates reveal a distinct orange/brown colour (white band “a” in Fig. 4 I and III). Younger agates either transmit the full visible light spectrum or produce a weaker brown colour (Fig. 4, IV). The difference is caused by the loss of the blue end of the visible light spectrum. Blue has a smaller wavelength and the transmission of white light through the well-developed plate edge-like structures results in the smaller wavelengths being bounced and scattered. Hence, the final transmitted light in the older agates is mainly from the larger wavelengths: orange/red giving this brownish colour. The poorly formed white bands in younger agates transmit more, or all, of the smaller visible wavelengths.

Fig. 2. Scanning electron micrographs showing a freshly fractured Lake Superior agate. The micrographs show an increasing magnification from (I) to (IV). Each higher magnification has focussed on the approximate centre of the previous image. In Fig. 2 (I), (a) is a globular region and (b) shows a most unusual weak white band that was not apparent in the hand specimen. High temperature dehydration of agate

Agate enthusiasts will be aware of the Brazilian enhydro(s) agates where bulk water has become trapped at the centre of the agate. Less well known is the fact that practically all agate contains water molecules that are free to enter and leave through structural pathways (Moxon, 2017). The ease of movement depends on the age of the agate and the surrounding water vapour pressure. In addition to free H2O, there is the less well-known silanol water (≡Si—OH). These silanol groups are found on the surface and within the agate structure. Strictly, silanol water is not water but the hydroxyl group. Agate is rich in these groups and, over the geological time scale, two neighbouring Si—OH groups combine to release water and form the Si—O—Si bond; this silanol water is often referred to as structural defect water. The total water content includes neighbouring silanol group water loss as well as free water and can be found by heating agate powders of less than 50 micron at temperatures greater than or equal to 1,000oC.

Evidence for the development of agate

My prime reason for examining property variations is to seek possible links between a particular property and the host rock age. Data plots of quartz crystallite size, density, moganite and total water content all show some valid regional links with respect to host rock age. Quartz crystallite size demonstrates the best accuracy and when plotted against host rock age, it demonstrates interesting development (Fig. 5a). The plot exhibits a four-stage agate development pattern for the first 450 Ma. Initially, there is 60 Ma of linear growth followed by growth cessation for the next approximate 200 Ma. Growth restarts for around 30 Ma followed by little change for the next 150 Ma. There is no further change with agates from hosts aged 1,100 Ma. Agates from Brazil (135 Ma host age) #10 and New Zealand (89 Ma) # 9 are clearly off trend: suggesting agate formation ages of 25 and 30 Ma respectively (data from Moxon and Carpenter, 2009).

Fig. 3. A well developed white band in an agate from Ethiebeaton quarry, Scotland (412 Ma). The sections at (c) show the typical plate-edge like structure with flat surfaces (d) where the plates have twisted. The micrograph is a montage assembly made from four individual micrographs.

The total water loss in agate with respect to host age has recently been investigated (Moxon, 2017). The study was able to demonstrate that the mean values of the total water show a linear decrease over the first 60 Ma (Fig. 5b). Other than the problematic New Zealand (89 Ma) agates, samples with a host age between 60 and 120 Ma were not available. Suitable agates of this age would have established the post 60 Ma trend. Extrapolation implies that agates between 60 and 120 Ma would lie somewhere between A and B (Fig. 5b). Lake Superior agates (approximately 1,100 Ma) are not shown but the total water is similar to the 180 Ma Botswana agates suggesting the total water content is independent of age for agates greater than 180 Ma. The outlier agates from Brazil # 10 and New Zealand # 9 indicate a formation age of 27 and 41 Ma respectively.

There is an increase in density over the first 55 Ma with stability over next 350 Ma (Fig. 5c). An upper point of density reference is shown by Madagascan macrocrystalline quartz at 2.647 gcm-3; although a more realistic density maximum for agate is provided by the smaller grain size in quartzite pebbles (d = 2.635 gcm-3; Fig. 5c). The density increases with age for the first 60 Ma and the outlier agates from Brazil # 10 and New Zealand # 9 suggest a formation age of 39 and 20 Ma respectively (Fig. 5c). Data from Moxon et al. (2006)

The relationship between moganite and host rock age is the final property (Fig. 5d). Once again, there is a cessation after 60 Ma with little change in the moganite content over the next 1,000 Ma. Unlike the total water plot, there is less room for doubt regarding moganite content in agates from hosts aged between 60 and 180 Ma. Extrapolation would suggest that agate from hosts greater than 60 Ma would have a moganite content closer to the approximately 4% found in agates from hosts older than 180 Ma. The outlier agates from Brazil #10 and New Zealand # 9 suggest formation ages of 25 and 40 Ma respectively (data from Moxon and Carpenter, 2009).

Fig. 4. (I) and (II) show 2mm thick slabs of Botswana agate (180 Ma host age) and New Zealand agate (89 Ma host age) respectively. The slabs are photographed in front of a reading lamp and the central white bands in the Botswana agate are dark brown (a) in the transmitted light (III). The diffuse white banding in the New Zealand agate shows as a pale brown colour (IV). Scale bars = 1cm. Summary of the evidence

1) All four plots in Fig. 5 indicate a cessation of change occurring after about 60 Ma. Given the moganite data plot, it is likely that total water in agates from hosts aged between 60 and 180 Ma would show a similar percentage water content to that found in hosts older than 180 Ma.

2) All four properties have demonstrated similar host age links. These properties show that agates generally form around the same geological age as the host. There are exceptions and the data shows that Brazilian and New Zealand agates have formed long after the host formation.

3) Agates from Brazil and New Zealand are outliers in all plots. The mean predicted formation age range of Brazilian and New Zealand agate using crystallite size, total water, and moganite content is within 25 to 27 and 31 to 43 Ma respectively. The density determinations have been excluded from these mean values; the predicted ages of 39 and 21 Ma for the Brazilian and New Zealand agates are respectively so much higher and lower than extrapolated data from the other three plots. The poor density values are due to the small density spread of only around 0.05 gcm-3 between the highest and lowest values: any minor errors have a large effect on the outcome.

4) The density and crystallite size show age-related increases..

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